(My pedicab, pre-foam-addition.)
Thanks to everybody who commented on my first post in this series: I’ve got great feedback, including a hilarious put-down from another local pedicabber (“Luke, Death Cab for Cutie called. They want a photo for the next album cover.”)
And, appropriately, there’s been a call for data. So here’s what I’ve got:
Here’s the exact analysis I sent to the City of Austin prior to my 4th meeting. (2.7 MB pdf) Not meant to be a conclusive, authoritative, automobile-worthy, or even well-formatted analysis, this was meant to show I’d put at least a little thought into the strength of the cab. The Telespar appendix mentioned in the analysis is available here.- Here are the pictures, as provided to the city before my meeting.
To address some safety issues raised, it’s useful to look at the style of pedicab in use by many other Austin pedicabbers: also no brakes, and attachment to the bike by a single bolt. There are even 20+ home-brews of this style on the Texas capitol’s streets. And, to be fair, I would estimate half of the licensed pedicabs are the far-fancier (and more expensive) 3-wheeled versions (one company making these, and another.) And good luck finding any materials analysis, even to the low level I’ve provided, from any pedicab manufacturer. It may exist, but the city certainly hasn’t sought it until I came up.
So, if I may conclude this post by being overly general:
- One ought to judge product quality not on the presence of a fancy marketing apparatus, but rather on the quantitative properties of a product.
- DIYers much smarter than I are developing important products, and early versions won’t always look pretty.
- Both consumers and makers miss out by labeling anything factory-made as safe and anything home-brewed as sketchy.
As always, any comments appreciated. Including put-downs about my pedicab, so long as they’re at least as funny as the Death Cab for Cutie one:)
84 thoughts on “My DIY Pedicab Saga: Just The Data”
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… and I think it’s probably safe, particularly for downtown Austin which isn’t exactly hilly. The problem is it doesn’t look safe, and the city of Austin is known for being difficult. The burden is on you to prove it’s safe, by having a thorough engineering analysis, I don’t just mean material strengths like in your report, but a static analysis of the design at least, taking into accounts forces and moments on all the joints. It’s not that the city even cares that much about safety, but if a customer is hurt in an accident with a commercial vehicle, they sue the manufacturer, if they are hurt in yours, they are going to sue the city for licensing it. A commercial vehicle provides them a legal cushion, your vehicle does not. It’s not about safety, it’s about liability. I’m not saying it’s right, just saying it is what it is.
Did you check with any legal council about their decision to terminate your talks with them about licensing your vehicle and their refusal to be recorded?
I don’t know why you can’t get the point of that “Death Cab” joke. Your cab obviously looks dangerous to some people. As you pointed out they DON’T have a problem with home-made stuff, but the examples you showed all looked professional and yes, SAFE. Yours could be nicknamed “The Mangler”. I’d be worried to lose a limb in that thing if you went off a curb or something. Come on you’ve got tape covering the sharp edges, it looks like something made in Junkyard Wars in 30 minutes. You have the skills, why don’t you just weld something with nice smooth edges and try submitting that. I bet they’d approve it. The inspector obviously doesn’t want something scary looking going around town making other people doubt he’s doing his job. The last thing he wants is complaints from “concerned citizens”. Have a little pride in your work man.
Have you looked into insurance for this thing? I can’t even imagine a reputable company insuring a vehicle like that for public transportation for many of the same reasons the city of Austin will not pass inspection on that thing (and probably more). Irregardless of how good of a job you personally feel you did assembling this thing, you need to prove that it is, in fact safe to carry passengers on. Pages of data sheets about the bolts you used and pictures of other odd DIY projects built with similar materials doesn’t really cut it…
Dude, quit arguing and hire an engineer to look over your design. We may be budding engineers, but we aren’t experienced.
The design document lists the materials and their strengths, but does not account for multiplication of forces such as in simple machines like levers. Looking at your homebrew bicycle trailer, it appears you have bolts connected to the ends of the square tubing rods, thus you have levers.
There are many other things to consider that may become safety hazards, but only an experienced engineer could tell you what those are. This thing may be ready to ride around your backyard, but not for making a profit.
Now I see why this story is on here in the first place, you write for make! Please, we don’t want to hear about how everyone’s out to get you and it’s some sort of conspiracy.
what’s that picture of the loft bed in your pdf from, from that book? i’m looking for different loft bed designs and that one looks streamline.
Dude, I wouldn’t ride that thing, either. As stated in the first article, it looks like some kids erector set project.
Go to a bike shop, and have them weld a proper frame for you. Your struggle will decrease exponentially with a professional looking pedicab.
Have you tried testing your cab? Try loading it with two 20 Gallon containers of water (same weight as two 160lb people) and riding it around for day covering as many miles as you think you would need to work on a busy day. You may find that at the end of that day many of the bolts are loosening. Not because the nuts are undoing, but because the tubes are not supported inside against the compression of the bolts and are being squashed flat, especially near the open ends of the tubes where they are much weaker.
It’s not that difficult to learn to MIG weld, (much easier if you only to tack a frame together and then take it to a professional welder.) A welded frame, with some triangulation, will definitely be stronger, lighter and safer.
I see several problems with your design.
First, the perforated tubing. These are designed to build static structures and not vehicles. No info is provided on impact resistance, and strength when bolted.
Second, the structure itself. everything is at square angles, which is dangerous (you seem to have covered the extremities with inner tubes fragments just to pass the regulations, not to actually protect the passengers and other road users), and weak structurally.
Third, the link between the bike and the seats is highly unstable. If you lean a little on the road, the weight of the trailer will pull you to the ground. Does it even qualify as a pedicab ? Looks like a simple trailer to me, but I’m not familiar with US regulations.
Fourth, do you really expect pad brakes on the bike (no brakes on the trailer form what I can see on the photos) to be able to stop your trailer with 2 people on it ? Think about braking while turning. Think about rain.
Fifth, the ¯|Â_ shaped structure. All the force is supported by a tiny surface of metal between the bolt and the inside of the perforations. It will fail quickly.
Sixth, your calculations are correct mathematically but do not make sense from an engineering point of view :
– Structural steel, page 7 : you assume yield strength is equal to joint strength. These are entirely different things. Surface of contact is not like continuous material.
– Bolts, page 8 : Each bolt is capable of 5580 lbs of shear strength. OK, but what does it say about the strength of the structure ? Nothing. From your photos it looks like the ¯|Â_ shaped structure is bolted about 10% from one end, which would create a x10 lever effect. Meaning only a 558 lbs-equivalent force on one end would break the bolt. And the tubing is probably weaker.
– Comparing the pure strength and thickness of steel used by other manufacturers does not make sense. The way steel is used is at least as important.
– On several instances you make a confusion between moment and movement, which illustrate your lack of knowledge in this matter.
– Etc.
In the current state, it is just normal for your design to be rejected.
@rich- Well Said.
Luke-
“One ought to judge product quality not on the presence of a fancy marketing apparatus, but rather on the quantitative properties of a product.”
– Yeah, like build quality, fit and finish maybe?
“DIYers much smarter than I are developing important products, and early versions won’t always look pretty.”
– But the one they present to the world will be their best. If this is truly your best, well, you now have a clue as to your skills…
“Both consumers and makers miss out by labeling anything factory-made as safe and anything home-brewed as sketchy.”
– only when it looks obviously home-brewed and sketchy.
@MasterShake916- you got that one right! But this post is a valuable tool that may stop other MAKErs with severly overestimated self evaluations of their talents from making themselves look foolish. That alone might MAKE DIY’ers appear more credible to the general public.
Or – God forbid – he rear end a car, causing the ¯|Â_ arm to fail at the joints and causing the passenger section to ultimately flip forward in a pole-vault kind of motion when that strut digs into the pavement. Or worse, think 40’s cars and their ‘impaler’ steering columns: the possibility of sending a nice piece of perforated steel tubing plunging backwards at chest/throat of an unsuspecting rider.
Also: notice the bar before and slightly above the passenger foot rest on the commercial models? That to keep someone’s foot from inadvertently sliding forward off the rest and risk getting caught between the pavement and the pedicab frame. With your design such a thing could certainly result in a snapped ankle, which from a customer experience point of view, would tend to put a real damper on repeat business.
As a lot of other folks have already said, dude, you’re really gonna need a welded frame. I imagine it will be rather difficult to get permitted otherwise.
Best of luck.
I might ride in this once because I thought it was funny. But I wouldn’t ride on it on a regular basis.
I wouldn’t trust that perforated steal at all. Especially at that L shaped support holding the cab to the bike. I’d worry I’d get that piece through my chest at in an accident.
It also looks like it’s got a serious potential for jack-knifing. Do all pedicabs work like that?
Why not consider this a prototype and go back with a more solidly built one?
I had a long post full of advice, but I came to a conclusion after watching your video. You seem to have a choice to make. Would you rather be right or would you rather drive your pedicab?
Don’t bother wasting good Make: blog space until you have this settled for yourself.
How you aren’t embarrassed when you watch that video is beyond me. With your “i did absolutely nothing wrong” attitude it’s as if you honestly expect other people to side with you. As you can see from probably close to 90% or more of the posts, that clearly is not the case. Here’s some “big people” advice Luke: Grow up. If you want the city of Austin to take you seriously, maybe you should act in a serious and professional manner. Dressing professionally, acting professionally, and providing proper documentation is a start. The safety essay that you complied yourself can hardly be taken seriously. You even hear it in the video when they request cad drawings so that an engineer can review them. And you act like this is absurd? You make claims that no one else has to go through this for their purchased pedicabs. Have you ever contacted a manufacturer and inquired about any sort of safety or structural documentation that they have? I’m willing to be that they have at least something…
While the steel may be strong enough, it looks like small bolts are bearing the majority of the stresses.
Suggestion:
Get a tubing bender and a small arc welder.
I opened the PDF, and assuming your calculations are correct abut the shear on the bolts… you’re going to exceed it handily the first time you hit something with the bike. Everything looks ok except for the gooseneck, and that… you have bolts in shear at the end of VERY long levers, and even if the bolts don’t get sliced right in two they will slowly hog the holes out; and the offset mounting method you’ve uses adds a torsional load to boot, which square tube absolutely *sucks* at.
You may not think you’re wrong, but you need to step out of the ego cloud and take a very, *very* close look at what you’ve got here. Hell, test it even: Mount two spars of grid together the same way and length you have there, mount one end vertically, and stand (you probably won’t even need to jump) on the other end. Oh, and be prepared to catch yourself on somethign.
You’re missing the point here Luke. Even if the city passed your pedicab, no one will ride in it. Further, no one will pay to ride in it. We’ve all made rubbish in the past, and we didn’t always see it at the time. This is rubbish. The whole thing. Spend some time on a better design. Spend some money on a better build. Sometimes you have to pay talented people to do things you aren’t familiar with or capable of. It’s ok. Remember, this isn’t a bristlebot, this isn’t burning man, this is about people’s lives. If the good people of Austin can’t trust your build, you don’t make any moolah.
Seriously, listen to what people are saying here.
As an engineer, I wouldn’t pass this thing either based on its massive number, scale, and obviousness of both structural and life/safety deficiencies and clear lack of its builders grasp of fundamental design theory. Just a few of the most basic problems have already been pointed out above quite well already by other engineers quite clearly, so I won’t bother to rehash them, only to second the analysis of the above posters.
More importantly, even were it to be perfectly structurally sound, I >still< wouldn't pass it simply due to its appearance. Sad fact of life, if it LOOKS like a liability issue, its actually a real liability issue, reality be damned. Show a picture of that to a jury of Joe Normals, and all the expert testimony in the world isn't going to sway them that the city was negligent (ie: liable) in allowing it on the road. The city, and any PE signing off on it both have very deep pockets so you know any attorney worth his beans would try to drag them into any suit related to this contraption, justified or not. Image problems do have unfortunate real-life consequences even if they ideally shouldn't. That and no passenger would ride in it, So the business plan is a big fail as well. You obviously have drive, so put some craftsmanship into it. Make something BETTER, lighter, sexier, or in any other was quantifiably superior to the commercial crap out there. THAT is what DIY is all about. If you can;t be bothered to do that, just give up and get a commercial bike.
less erector set, more welding.
i’d only ride this if it was free, i was drunk off my ass, you supplied a helmet, and if my car was parked on red river and 6th and you picked me up at el camino.
I’m a mechanical design engineer, I’ve built bikes, I’ve taught welding; I think I’m qualified to comment on your project. I’ve built and ridden on things like your pedicab. They’re a lot of fun. I’ve never asked anyone to ride on them, they volunteered. I’ve never sought certification for them.
What you have is a crude prototype and a pdf. What you don’t have is a product on which you can build a company. You don’t have an analysis of the system, but a back of the envelope calculation of a couple parameters, nor do you have any testing that says that your pedicab is roadworthy. The discussion in your pdf displays a shocking degree of arrogance and little understanding of what an inspector would be looking for – it inspires no faith in the inspector that your project is safe and should be approved.
What you don’t have is an understanding of what you are doing. Are you trying to start a pedicab business, manufacture pedicabs, or design pedicabs? Those are three very different businesses.
(I also have to say, buying a welder without learning how to weld properly and safely is not a good idea. Galvanized steel is deadly to weld.)
How much have you tested this thing anyway? Riding it around is not testing. Strapping a couple hundred pounds in it and running into a wall at speed is testing. Hard corners on wet surfaces, dry surfaces, and wet-dry surfaces is testing it. How harsh should testing be? Look at it this way, if you run into the back of some car, and a passenger is impaled on a sawed off piece of strut, how is that going to play out? Frankly, if you haven’t broken it, you haven’t tested it.
Building good stuff is hard, really hard. But there’s not a maker who’s advancing the field who hasn’t put in their dues. You build it, you test it, you break it, you fix it, lather, rinse repeat. After a dozen iterations, you’ll start to see why experts are expert, why authorities deserve respect.
# DIYers much smarter than I are developing important products, and early versions won’t always look pretty.
Every company that develops through prototypes makes ugly early versions. The difference between you and them is that their early versions are prototypes that don’t get into production. They are tested, improved and scrapped before the final production version is ready.
That contraption you have built looks dangerous and uncomfortable to ride in. Do you have a 90 degree angle between seat and back rest? The bike will be unsafe to operate with two adults on the trailer. During a turn the trailer will push your bike over, because the hinge is located so high above the ground. Take a look at some commercial bike trailers (big and small) and copy the good features. Put the hinge near the rear axle of the bike and you will greatly increase stability. You will also be able to remove the two weak points from the shaft (the 90 degree angles).
Get a bike with disc brakes. Discs work better when wet and can handle higher loads than rim brakes. Rim brakes are notoriously lousy when wet.
What you’ve got now is a hack. With the help you’ve been given, you must turn it into a prototype and then into the final pedicab you are going to present to the city officials. You still have a long way to go. Scrapping this hack is not time wasted. It is time spent learning. If you go on pushing this hack to the city officials you will only waste time. Stop wasting time and go back to learning stuff.
How many strain gages have you bonded to that thing? Who did the vibrational analysis? How long before that structural steel street sign post material fatigues? Under normal dynamic loads and vibration levels, how long before those bolts come loose? How long before they wear through?
If you can’t answer these questions, you need to start thinking about why that is.
I reviewed your documents and they are far from an engineering analysis. An engineering analysis is generally done by a qualified engineer. I can see the amount of effort you’ve put into this, and I commend you for it, but you need to do it right. Use your whole ass, as they say (don’t do it half assed), and talk to an engineering services firm. You’ll pay out the nose for it, but you’ll get it done right.
I’d have to agree with the majority of the comments on everything to do with your project. You need to work with these people as opposed to feel like they’re out to get you. Don’t just film people because you can, even if you can, ask permission, it’s general courtesy!!!
Design a proper product, that means a tubular welded frame, brakes, the lot. Design the best pedicab you can, your company could be known for having the best, safest pedicabs on the streets. Think of this as an opportunity to learn from your mistakes and produce a better product.
Even with an engineers stamp if the design was improved, I think not allowing some so un-finished ‘looking’ is a problem for a governing body. If they allow something that looks SO DIY then they will have a harder time easily identifying the illegal DIY bum that built his death cab out of rejected parts from the scrap bin.
They let individuals get away with all kinds of wacky modifications to automobiles, making rail cars and dune buggys and so on … but they don’t let them be used as a taxi!
I hate to say this, but that is a prototype for an uncontrollable trailer, not a pedicab. When this story first started, I figured you had something that was a real pedi-cab (welded steel tube frame, common axle with a disk brake on the trailer, tail-lights & turn signals, “doubler” chain ring, etc.), not a lashed-up structural collapse accident looking for a place to happen.
Just from a general safety viewpoint, here’s some things that just jump to mind:
– No brakes on the trailer body.
– Static loading tube.
– Lash-up with bolts at 90 degree angles.
– Attaches to your seat post?
– Lights & Reflectors?
Make: You wasted how much bandwidth on this guy?
You have plenty of good engineering advice here. I am going to give you some procedural advice: stop being a prick.
The best way to get what you want from government officials is to cooperate. They have something you want (the license), and you can’t force them to give it to you; you have to make them want to give the license to you. Acting like a jerk will do the opposite, and any good bureaucrat, when sufficiently motivated, can make sure you never get that license, no matter what you do.
If you really want a pedicab license — and your attitude makes me suspect that is not your main objective — when you go back to the city inspectors, the best thing to start with would be an apology … whether you mean it or not.
I’m late to the game here, but here’s my 2 cents (and I’m a former 15-year Austin resident, so I know how City Hall can be…)
Ditch the perforated square steel tubing, and weld up a proper frame from tubular steel. I see each one of those perforations as a (potential) stress riser and failure point.
Nothing says “I’m taking this seriously” like a welded-up frame. What your contraption says is, “I’m trying to get this out the door as quickly as possible.”
Just because you can do something doesn’t mean you should.
crash test!
vidz plz
You suck @ build, son.
But I think its time to re-evaluate.
Correcting you’re “engineering” isn’t even worth my time. Your shear strength estimates are off for starters (yes that’s what efunda says but you’re using it wrong). When you know what you did wrong, go ahead and post again. But until then stay off the streets and stay off MAKE. I used to really love this site…
I expect better reporting from Make. I read the magazine and this blog because it presents interesting projects and thought-provoking ideas. While I admit that this article provoked thought, it’s not the kind that I’d like to see from Make. At the risk of being overly general, I don’t want to see more articles like this one.
This isn’t anti-Maker discrimination. This is a case of bad design, poorly implemented. Had this been presented in a different way, I might have a more neutral reaction (for example, as a call for help to improve or critique the design).
After watching this guy wield a sawzall to make a “chicken tractor” I do hope that he gets some serious training before playing with serious tools. Make friends with the engineering dept at your local 4-year university and have a bunch of smart students come up with a design that they think is safe. They can give the design to 3rd world countries to fab up for their local use, and you can use the design to run your pedalcab business.
Get some good tools, good materials, and good training. Then start building. Otherwise, you might want to re-evaluate the reasons why all of the commercially available pedalcabs are so expensive.
Now, I’m no structural or mechanical engineer, but even I can recognize a bad design when I see it. The most obvious and dangerous looking problem being those joints… jesus man, didn’t you ever play with legos/erector/meccanos? You know all the times those crappy joints on your toys broke or came loose? Yeah, that happens in real life too.
Seriously though. Perforated tubing? Shameful.
I’m sure if you try harder you will succeed, but for the good of all DIYers, please don’t be half-assed about it. Half-assery gets us nowhere.
“this was meant to show I’d put at least a little thought into the strength of the cab.”
A little thought is not going to get it certified. The public and the government need indisputable proof to show that it is safe and strong and will not fail during normal use. A little thought is exactly the recipe for disaster that can get you, the city, and whoever else involved sued, particularly in such a litigation-happy world.
And please stop posting these until you get a design that is:
a) Safe
b) Professional
c) Certified
I conquer with the sentiments of the above comments. With the padding off, it looks worse. That block you’re using to go 90 degrees at the top of the -|_, will take the force and apply a torque. Not good at all.
It is my opinion that they are right to deny you your permit. Hire an engineer to design something, and have it welded by a ticketed welder. That’s all there is to be said about this. I’m sorry if it hurts your ego, but this just isn’t good enough.
I saw 2 of these pieces of S last night.
Look Luke, I’m a pedicabber too and it’s not that I don’t have the balls to say this to your face, but I just don’t want it to be a defensive angry arguement. We have your side of it right here. You’ve provided all the (in your own words possibly innaccurate) information for everyone to see. All the engineers say it’s unsafe. All the veteran pedicabbers say it’s unsafe.
We aren’t afraid of you infrnging on our business. We’re not jealous of your DIYness, we are afraid that you are going to seriously hurt someone.
So I have two pieces of advice.
1.You’ve made your $600 back (the price of $300 per cab listed in the chronicle), considering you had it at ACL, you probably made a lot more and you didn’t pay lease that whole time. Quit while you’re ahead.
2.If you won’t relent, as I’m fairly sure you won’t, then go around to every pedicabber next time you work and ask them what they honestly think. I know you think you’re right, but virtually everyone in the Austin pedicab scene thinks you’re endangering the industry and worse, the people of Austin.
It’s not a jealousy thing. Ken made his own cab and it rocks. Ken started taking credit cards and a couple more people have followed that example, and it seems to be paying off for them with no bad blood from other pedicabbers. This is an obvious advantage for them above all the others and noone is upset about it.
I’m really trying to make you understand. All this bad blood is not because we’re jealous. We want you to succeed at being liberated from paying lease. We want you to DIY a great piece of machinery any of us would be proud to ride. This just isn’t it. Please, for the good of the industry and the safety of passengers, consider returning to lease paying until you can produce something that passes inspection.
boy does that suck. your a complete retard. you have no style or class. plus, youve wasted all this time on the internet and arguing your blatently errored point of view, that you could have been using your time to build a REAL road worthy pedicab. this is garbage. please go find a real job or go back to school and pay attention this time.
Anybody that thinks paying some company like Main Street Pedicab $4000 for a f**king base model makes more sense than DIY is L to the D. Most of these dudes that play “hipster trike police” & cop an arrogant attitude about custom trikes because they rent and you own. Bottom line. Judging you for your ingenuity makes them feel better about their conformity. I know one thing, that “death cab” appears to be made primarily of uni-strut, which is rated for an INCREDIBLE amount of weight…WAY MORE than ANY commercially produced pedicab frame (take it from a guy that had to reinforce a commercially produced pedicab frame).
The only chinks I see in your armor is the lack of a second point of contact from the carriage to the bike, and the brakes NEED to be in the back. Keep your head up!